RU2768097C1 - Projection unit for head-up display (hud) with p-polarized radiation - Google Patents

Abstract

FIELD: automotive industry.

SUBSTANCE: invention relates to a projection device for a head-up display - a head-up display (HUD) with p-polarized radiation. It contains at least: laminated glass with a HUD zone, containing an outer sheet and an inner sheet, which are connected to each other by a thermoplastic intermediate layer; an electrically conductive coating on the surface facing the intermediate layer of the outer sheet or the inner sheet or in the intermediate layer; and a projector aimed at the HUD area (B); wherein the radiation of the projector is p-polarized, and the laminated glass with an electrically conductive coating in the entire spectral range of 450-650 nm has a degree of reflection of p-polarized radiation of at least 10%, and the electrically conductive coating contains at least three electrically conductive layers, each of which is between two dielectric layers or sequences of dielectric layers, and the sum of the thicknesses of all electrically conductive layers is not more than 30 nm,
and while the electrically conductive layers have a thickness of from 5 nm to 10 nm.

EFFECT: invention provides obtaining a laminated glass of a projection device without a wedge-shaped film and containing an electrically conductive coating, which can also be used as a heated coating, while the HUD projection has a high intensity, the glass has a high light transmission and a pleasant appearance.

12 cl, 5 dwg, 2 tbl

Description

The invention relates to a projection device for a projection display (windshield display) and to its use.

Modern cars are increasingly equipped with so-called head-up displays (HUDs). With the help of a projector, as a rule, in the dashboard area, images are projected onto the windshield, which are reflected there and perceived by the driver as a virtual image (seen by him) behind the windshield. In this way, important information, such as current speed, navigation or warning information, can be projected into the driver's field of view, which the driver can perceive without taking his eyes off the road. Thus, head-up displays can make a significant contribution to improving road safety.

HUD projectors operate predominantly with s-polarized light and illuminate the windshield at an incidence angle of about 65°, which is close to the Brewster angle for air-to-glass transition (57.2° for soda-lime glass). This raises the problem that the projector image is reflected from both outer surfaces of the windshield. Because of this, in addition to the desired main image, a slightly offset side image appears, the so-called ghost image (Ghost). This problem is usually solved by placing the surfaces at an angle to each other, in particular by using a wedge-shaped intermediate layer for laminating windshields made in the form of laminated glass, so that the main image and the phantom image are superimposed on each other. Laminated glasses with wedge-shaped films for HUDs are known, for example, from WO2009/071135A1, EP1800855B1 or EP1880243A2.

Wedge-shaped films are not cheap, so the manufacture of such laminated glass for HUD is quite expensive. Therefore, there is a need for HUD projection devices in which windshields do not contain wedge-shaped films. So, for example, you can have a HUD projector work with p-polarized radiation, which is weakly reflected from glass surfaces. Instead of films as a reflection surface for p-polarized radiation, the windshield contains an electrically conductive coating. Document DE10/2014 220189A1 describes such a HUD projection device that operates with p-polarized light. As a reflective structure, among other things, a single metal layer with a thickness of 5 nm to 9 nm, for example, from silver or aluminum, is proposed.

More sophisticated electrically conductive windshield coatings are also known, which are used, for example, as IR reflective coatings to reduce the heating of the vehicle interior and thereby increase thermal comfort. However, the coatings can also be used as heated coatings if they are connected to a voltage source so that current flows through the coating. Suitable coatings comprise conductive metal layers, in particular based on silver. Since these layers are susceptible to corrosion, they are usually applied to the surface of the outer sheet or inner sheet facing the intermediate layer so that they do not come into contact with the atmosphere. Silver-containing transparent coatings are known, for example, from documents WO03/024155, US2007/0082219A1, US2007/0020465A1, WO2013/104438 or WO2013/104439.

If a conductive coating is to be used on the one hand as an IR reflective or heated coating and on the other hand as a reflective surface for a HUD, then high demands are placed on its optical and electrical properties. Thus, in particular, at the same time the surface resistance must be sufficiently low, the light transmission sufficiently high, the reflectivity of the HUD projector radiation must be sufficiently high, and the reflection color must be relatively neutral.

The invention is based on the task of developing an improved projection device for a projection display. The laminated glass of the projection device must not contain a wedge-shaped film and must have an electrically conductive coating, which can also be used, in particular, as a heated coating. The HUD projection should be created with high intensity, and the laminated glass should have high light transmission and pleasing appearance.

According to the invention, the object of the present invention is achieved by the projection device according to claim 1. Preferred embodiments are indicated in the dependent claims.

According to the invention, p-polarized radiation is used to create a HUD image, and the laminated glass contains an electrically conductive coating that sufficiently reflects p-polarized radiation. Because HUD projection devices typically have an angle of incidence of about 65°, fairly close to the Brewster angle for an air-to-glass transition (57.2°, soda-lime glass), p-polarized radiation is almost not reflected from glass surfaces, but is reflected mainly from a conductive coating. Therefore, ghost images do not occur or are barely visible, so that the use of an expensive wedge-shaped film can be dispensed with.

The coating according to the invention has relatively thin conductive layers, in particular silver layers, compared to the conventional coatings used up to now. So that also makes windows cheaper. However, the inventors have found that too thin conductive layers lead in turn to an increase in light absorption and a decrease in the transparency of the laminated glass. This was unexpected and intuitively incomprehensible, since a decrease in the thickness of the conductive layers should have led to an increase in transmission. The conductive layers according to the invention are thick enough to avoid this effect. Despite the thin layers, the coating is nevertheless suitable for reflecting p-polarized radiation with sufficient intensity to create a HUD image and for use as a heated coating, especially when using 40-50V voltage sources common in the field of electric vehicles. The optical requirements of the windshield, in particular with regard to transparency and color, can also be met. This is a great advantage of the present invention.

A projection device for a head-up display (HUD) according to the invention includes at least one electrically conductive laminated glass and a projector. As usual for a HUD, the projector irradiates the area of the windshield where the radiation is reflected in the direction of the viewer (driver), resulting in a virtual image that the viewer sees as being behind the windshield. The area of the windshield illuminated by the projector is called the HUD area. The direction of the projector's beam can usually be changed using mirrors, in particular vertically, in order to adapt the projection to the size of the viewer's body. The area in which the observer's eyes should be relative to the position of the mirror is called the eye box window. By adjusting the mirror, this eye box can be shifted vertically, with the resulting area available (i.e. the overlap of all possible eye boxes) being referred to as the "eye box". An observer located inside the eye zone can perceive a virtual image. This means, of course, that the eyes of the observer, and not the whole body, should be located in the eye zone.

The HUD terms used herein are generally known to those skilled in the art. For a detailed description, please refer to Alexander Neumann's dissertation "Simulation-based measurement technology for testing projection displays", in particular chapter 2 "Projection display", Institute for Informatics of the Technical University of Munich (Munich: University Library of the Technical University of Munich, 2012) .

Laminated glass contains an outer sheet and an inner sheet, which are connected to each other by an intermediate thermoplastic layer. The laminated glass is provided for separating, in a window opening, in particular a window opening of a vehicle, the interior from the outside. The inner sheet in the context of the invention refers to facing inside (in particular, in the interior of the car) sheet of laminated glass. An outer sheet is a sheet facing the external environment. The laminated glass is preferably a vehicle windshield (in particular an automobile windshield, such as a car or truck).

Laminated glass has a top edge and a bottom edge, as well as side edges located between them. The top edge is the edge that points upwards in the mounted position. The bottom edge is the edge that points downwards in the mounted position. The top edge is often also referred to as the roof edge and the bottom edge as the engine edge.

The outer sheet and the inner sheet have outwardly and inwardly facing surfaces and a peripheral side edge located therebetween. The outer surface in the context of the invention is the main side, which in the mounted state will face the external environment. The inner surface in the context of the invention is the main side, which in the assembled state will face the passenger compartment. The inner surface of the outer sheet and the outer surface of the inner sheet face each other and are bonded to each other by a thermoplastic interlayer.

The laminated glass has an electrically conductive coating, in particular a transparent electrically conductive coating. The electrically conductive coating is preferably applied to the surfaces facing the intermediate layer of both glass sheets, ie to the inner surface of the outer sheet or the outer surface of the inner sheet. Alternatively, the electrically conductive coating may also be present within the intermediate thermoplastic layer, for example on a carrier film sandwiched between two thermoplastic adhesive films. The conductive coating can be provided, for example, as an IR-reflective solar control coating or as a heated coating that has an electrical contact and is heated by the flow of current. By transparent coating is meant a coating which has an average visible transmittance of at least 70%, preferably at least 80%, and which thus does not significantly restrict the view through the glass. Preferably, at least 80% of the glass surface is provided with a coating according to the invention. In particular, the coating is applied to the entire surface of the glass, except for the peripheral edge zone and, optionally, local zones, which, as places for communication, sensors or cameras, must ensure the transmission of electromagnetic radiation through the laminated glass and are therefore not provided with a coating. The width of the uncoated peripheral edge zone is, for example, up to 20 cm. It prevents direct contact of the coating with the surrounding atmosphere, so that the coating inside the laminated glass is protected against corrosion and damage.

An electrically conductive coating is a set or sequence of layers containing several electrically conductive, in particular metal-containing layers, with each electrically conductive layer sandwiched between two dielectric layers or series of dielectric layers. Thus, the coating is a thin layer system of n electrically conductive layers and ( n + 1 ) dielectric layers or sequences of dielectric layers, where n is a natural number, and the lower dielectric layer or sequence of dielectric layers is always alternately followed by a conductive layer and a dielectric layer or sequence dielectric layers. Such coatings are known as solar control coatings and heated coatings, with the electrically conductive layers typically being silver based.

The electrically conductive coating according to the invention is formed in such a way, in particular by choosing the materials and thicknesses of the individual layers, as well as by structuring the succession of dielectric layers, that the coated laminated glass in the entire spectral range of 450-650 nm has a p-polarized radiation reflectance of at least 10 %. This means that in the spectral range 450-650 nm there are no points with a reflection degree of less than 10%. This creates a projected image of sufficiently high intensity. Preferably, the degree of reflection of p-polarized radiation in the entire spectral range of 450-700 nm, particularly preferably in the entire spectral range of 450-800 nm, is at least 10%.

The degree of reflection describes the proportion of reflected radiation from the total emitted radiation. It is indicated in % (based on 100% of the emitted radiation) or as a dimensionless number from 0 to 1 (normalized to the emitted radiation). If it is depicted as a function of wavelength, a reflection spectrum is formed.

In one preferred embodiment, the electrically conductive coated laminated glass has a p-polarized reflectance of at least 12%, preferably at least 13% over the entire spectral range of 450-650 nm. For example, the degree of reflection of p-polarized radiation is in the entire spectral range 450-650 nm from 10% to 20%, preferably from 12% to 17%, in particular from 13% to 15%. The degree of reflection in this range can be easily achieved with the coating according to the invention and is high enough to create a high intensity HUD projection.

The average value of the degree of reflection of p-polarized radiation in the entire spectral range of 450-650 nm is preferably from 10% to 20%%, preferably from 12% to 17%, in particular from 13% to 15%. To achieve the most color-neutral display of the projector image, the reflection spectrum should be as smooth as possible and not have pronounced local minima and maxima. In the spectral range 450-650 nm, the difference between the maximum observed reflectance and the average reflectance, as well as the difference between the minimum observed reflectance and the average reflectance (based on 100% of the emitted radiation) in the preferred embodiment should be no more than 5 %, particularly preferably not more than 3%, highly preferably not more than 1%.

In the context of the present invention, the above with respect to the degree of reflection of p-polarized radiation refers to the reflectance measured at an angle of incidence of 65° to the normal to the inner surface. The data on the degree of reflection or the reflection spectrum refer to a reflection measurement with a light source that, in the considered spectral range, emits homogeneous radiation with a normalized radiation intensity of 100%.

The projector is placed against the inner side of the laminated glass and irradiates the laminated glass through the inner surface of the inner sheet. It aims at the HUD area and irradiates it to create a projection on the windshield. According to the invention, the radiation from the projector is p-polarized, preferably substantially purely p-polarized, i.e. the proportion of p-polarized radiation is 100% or only slightly deviates from this value. As a result, a particularly intense HUD image is created and ghost images can be avoided. In this case, the indication of the direction of polarization refers to the plane of incidence of radiation on the laminated glass. p-Polarized radiation is radiation whose electric field oscillates in the plane of incidence. s-Polarized radiation is radiation whose electric field oscillates in a plane perpendicular to the plane of incidence. The plane of incidence is generated by the incidence vector and the normal to the laminated glass surface at the geometric center of the HUD area.

The radiation from the projector is incident on the laminated glass at an angle of incidence preferably between 45° and 70°, in particular between 60° and 70°. In one preferred embodiment, the angle of incidence differs from the Brewster angle by no more than 10°. In such a case, p-polarized radiation is only slightly reflected from the surfaces of the laminated glass, so that no ghost image occurs. The angle of incidence is the angle between the projector's beam direction vector and the inner surface normal (ie, the normal to the inwardly facing outer surface of the laminated glass) at the geometric center of the HUD area. The Brewster angle for the air-to-glass transition for soda-lime glass, which is commonly used for window panes, is 57.2°. Ideally, the angle of incidence should be as close to the Brewster angle as possible. However, it is also possible to use, for example, an angle of incidence of 65°, which is typical for projection HUD devices, which can be implemented without problems in vehicles and which differs only slightly from the Brewster angle, so that the reflection of p-polarized radiation is only slightly increased.

Since the reflection of the projector's radiation comes mainly from the reflective coating and not from the outer surfaces of the glass sheet, it is not necessary to angle the outer surfaces of the glass to each other to avoid a ghost image. Therefore, the outer surfaces of the laminated glass are preferably arranged substantially parallel to each other. To this end, the intermediate thermoplastic layer and the inner and outer glass sheets are preferably not wedge-shaped, but with a substantially constant thickness, in particular also in the vertical direction between the upper and lower edge of the laminated glass. On the contrary, the wedge-shaped intermediate layer would have a variable, in particular increasing, thickness in the vertical direction between the lower and upper edges of the laminated glass. The intermediate layer is usually formed from at least one thermoplastic film. Because standard films are significantly less expensive than wedge-shaped films, the production of laminated glass becomes cheaper.

According to the invention, the electrically conductive coating comprises at least three electrically conductive layers, wherein the sum of the thicknesses of all electrically conductive layers does not exceed 30 nm. In one preferred embodiment, the sum of the thicknesses of all electrically conductive layers is between 15 nm and 30 nm, preferably between 20 nm and 25 nm. The thickness, or layer thickness, in the context of the present invention refers to the geometric and not to the optical thickness, which is the product of the refractive index and the geometric thickness. This is particularly advantageous in terms of cost savings and meeting requirements for reflectance and other optical properties. In one particularly preferred embodiment, the number of electrically conductive layers is exactly three. In principle, more complex layer structures are not required to achieve the desired coating characteristics. With three electrically conductive layers and an appropriate number of dielectric layers or layer sequences, there is a sufficient degree of freedom to optimize the coating in terms of transmission and reflection characteristics as well as coloration.

According to the invention, the electrically conductive layers, in particular all electrically conductive layers, have a thickness of 5 nm to 10 nm, particularly preferably 7 nm to 8 nm. Layer thicknesses in these ranges are particularly well suited to achieve the desired coating properties. In particular, the conductive layers are thick enough not to lead to increased absorption of visible light, which unexpectedly occurs in the case of too thin conductive layers.

The electrical conductivity of the coating is provided by functional electrically conductive layers. By dividing all the conductive material into several separate layers, each of them can be made thinner, which will increase the transparency of the coating. Each electrically conductive layer preferably contains at least one metal or metal alloy, such as silver, aluminium, copper or gold, and is particularly preferably based on a metal or metal alloy, i.e. essentially consists of a metal or metal alloy, except for possible doping or impurities. Preferably, silver or a silver-containing alloy is used. In one preferred embodiment, the electrically conductive layer contains at least 90 wt.% silver, preferably at least 99 wt.% silver, particularly preferably at least 99.9 wt.% silver.

According to the invention, between the electrically conductive layers, as well as under the lowest conductive layer and above the uppermost conductive layer, there are dielectric layers or a series of dielectric layers. Each dielectric layer or sequence of dielectric layers contains at least one anti-reflective layer. Anti-reflective layers reduce the reflection of visible light and thus increase the transparency of the coated glass. Anti-reflection layers comprise, for example, silicon nitride (SiN), mixed silicon and metal nitride such as silicon-zirconium nitride (SiZrN), aluminum nitride (AlN) or tin oxide (SnO). In this context, mixed silicon and metal nitrides are particularly preferred. In addition, the anti-reflection layers may be doped. The thickness of the individual anti-reflection layers is preferably 10 nm to 100 nm, in particular 20 nm to 80 nm.

In turn, the anti-reflection layers can be divided into at least two sublayers, in particular, a dielectric layer with a refractive index less than 2.1 and an optically highly refractive layer with a refractive index greater than or equal to 2.1. The sequence of these two sublayers can in principle be chosen arbitrarily, with the optically highly refractive layer being preferably located above the dielectric layer, which is particularly advantageous in terms of surface resistance. The thickness of the optically highly refractive layer is preferably 25% to 75% of the total thickness of the anti-reflection layer. The optically highly refractive layer with a refractive index greater than or equal to 2.1 contains, for example, MnO, WO ₃ , Nb ₂ O ₅ , Bi ₂ O ₃ , TiO ₂ , Zr ₃ N ₄ and/or AlN, preferably contains mixed silicon and metal nitride , for example, mixed silicon and aluminum nitride, mixed silicon and hafnium nitride or mixed silicon and titanium nitride, especially preferably mixed silicon and zirconium nitride (SiZrN). The dielectric layer with a refractive index of less than 2.1 preferably contains at least one oxide, for example tin oxide, and/or a nitride, particularly preferably silicon nitride.

In one preferred embodiment, one or more series of dielectric layers, preferably each series of dielectric layers contains a first matching layer, which is under the electrically conductive layer. The first matching layer is preferably above the anti-reflection layer. The first matching layer is preferably directly below the electrically conductive layer so that it is in direct contact with the conductive layer. This is particularly advantageous from the point of view of the crystallinity of the electrically conductive layer.

In one preferred embodiment, one or more series of dielectric layers, preferably each series of dielectric layers contains a smoothing layer, which is between two electrically conductive layers. The smoothing layer is located under the first matching layer, preferably between the anti-reflection layer and the first matching layer, if such a first matching layer is present. The smoothing layer is particularly preferably in direct contact with the first matching layer. The smoothing layer leads to an optimization, in particular a smoothing of the surface for the electrically conductive layer later applied above. An electrically conductive layer deposited on a smoother surface has a higher light transmission coefficient with a lower surface resistance at the same time. The thickness of the smoothing layer is preferably 3 nm to 20 nm, particularly preferably 4 nm to 12 nm, highly preferably 5 nm to 10 nm, for example about 7 nm. The smoothing layer preferably has a refractive index of less than 2.2.

The smoothing layer preferably contains at least one non-crystalline oxide. The oxide may be amorphous or partially amorphous (and thus semi-crystalline), but not fully crystalline. The non-crystalline smoothing layer has a low roughness and thus forms a preferred smooth surface for layers applied above the smoothing layer. In addition, the non-crystalline smoothing layer improves the surface structure of the layer deposited directly on the smoothing layer, preferably the first matching layer. The smoothing layer may contain, for example, at least one oxide of one or more elements selected from tin, silicon, titanium, zirconium, hafnium, zinc, gallium and indium. Particularly preferably, the smoothing layer contains a non-crystalline mixed oxide. Highly preferably, the smoothing layer contains a mixed oxide of tin-zinc (ZnSnO). The mixed oxide may be doped. The smoothing layer may comprise, for example, an antimony-doped mixed tin-zinc oxide. The mixed oxide preferably has a substoichiometric oxygen content. The proportion of tin is preferably 10 to 40% by weight, particularly preferably 12 to 35% by weight.

In one preferred embodiment, one or more sequences of dielectric layers contains a second matching layer that is above the electrically conductive layer, preferably each sequence of dielectric layers contains such a layer. The second matching layer is preferably under the anti-reflection layer.

The first and second matching layers lead to an improvement in the surface resistance of the coating. The first matching layer and/or the second matching layer preferably contains zinc oxide ZnO _1-δ with 0≤δ≤0.01. The first matching layer and/or the second matching layer is more preferably doped. The first matching layer and/or the second matching layer may comprise, for example, aluminum doped zinc oxide (ZnO:Al). The zinc oxide is preferably deposited substoichiometric with respect to oxygen to prevent excess oxygen from reacting with the silver containing layer. The thicknesses of the first matching layer and the second matching layer are preferably 3 nm to 20 nm, particularly preferably 50 nm to 15 nm, highly preferably 8 nm to 12 nm, in particular about 10 nm.

In one preferred embodiment, the electrically conductive coating comprises one or more blocking layers. Preferably, at least one, particularly preferably each, electrically conductive layer corresponds to at least one blocking layer. The blocking layer is in direct contact with the electrically conductive layer and is directly above or immediately below the electrically conductive layer. Thus, there are no other layers between the electrically conductive layer and the blocking layer. The blocking layer may also be located directly above and directly below the conductive layer. The blocking layer preferably contains niobium, titanium, nickel, chromium and/or alloys thereof, particularly preferably nickel-chromium alloys. The thickness of the blocking layer is preferably 0.1 nm to 2 nm, particularly preferably 0.1 nm to 1 nm. The blocking layer immediately below the electrically conductive layer serves in particular to stabilize the electrically conductive layer during heat treatment and improves the optical quality of the electrically conductive coating. The blocking layer immediately above the electrically conductive layer prevents the sensitive electrically conductive layer from contacting an oxidizing atmosphere during the deposition of the next layer, eg the second matching layer, by reactive cathode sputtering.

If the first layer is higher than the second layer, this means in the context of the invention that the first layer is further from the coated substrate than the second layer. If the first layer is below the second layer, this means in the context of the invention that the second layer is further from the substrate than the first layer. If the first layer is above or below the second layer, this does not necessarily mean in the context of the invention that the first and second layers are in direct contact with each other. Unless explicitly excluded, there may be one or more other layers between the first and second layers. The indicated values of the refractive index are measured at a wavelength of 550 nm.

In one preferred embodiment, between the two electrically conductive layers (21) is a series of dielectric layers, including:

- anti-reflective layer (22) based on silicon nitride (SiN), mixed silicon nitride and metal, such as silicon-zirconium nitride (SiZrN), aluminum nitride (AlN) or tin oxide (SnO), preferably based on mixed silicon and metal nitride,

- a smoothing layer (23) based on an oxide of one or more elements selected from tin, silicon, titanium, zirconium, hafnium, zinc, gallium and indium,

- the first and second matching layer (24, 25) based on zinc oxide and

optionally, a blocking layer (26) based on niobium, titanium, nickel, chromium and/or their alloys.

In this case, a specific order of layers is not required. Below the lowermost conductive layer and above the uppermost conductive layer, there is preferably an antireflection coating and a matching layer based on the above preferred materials. The already mentioned preferred thickness ranges for the individual layers apply.

The electrically conductive coating with reflective characteristics according to the invention can in principle be realized in various ways, preferably using the layers described above, so that the invention is not limited to a particular sequence of layers. A particularly preferred embodiment of the coating is shown below, with which particularly good results are achieved, in particular at a typical angle of incidence of about 65°.

The electrically conductive coating comprises at least three, in particular exactly three electrically conductive layers, preferably based on silver, each electrically conductive layer having a thickness of 5 nm to 10 nm, in particular 7 nm to 8 nm. Next, the electrically conductive layers are numbered starting from the substrate on which the coating is deposited. The sequence of dielectric layers below the bottommost conductive layer, above the topmost conductive layer and between the conductive layers always contains an anti-reflective layer, preferably based on a mixed silicon nitride and a metal such as silicon-zirconium nitride or silicon-hafnium nitride. The anti-reflection layer below the first conductive layer has a thickness of 15 nm to 25 nm, particularly preferably 20 nm to 24 nm. The anti-reflection layer between the first and second conductive layers has a thickness of 25 nm to 40 nm, preferably 30 nm to 35 nm. The anti-reflection layer between the second and third conductive layers has a thickness of 70 nm to 90 nm, preferably 75 nm to 80 nm. The anti-reflection layer above the third conductive layer has a thickness of 35 nm to 45 nm, preferably 37 nm to 42 nm.

In a highly preferred embodiment, the electrically conductive coating comprises, starting from the substrate, the following sequence of layers, or consists of it:

- an anti-reflection layer with a thickness of 15 nm to 25 nm, preferably 20 nm to 24 nm, preferably based on a mixed silicon and metal nitride, such as silicon-zirconium nitride or silicon-hafnium nitride,

- a first matching layer with a thickness of 5 nm to 15 nm, preferably 8 nm to 12 nm, preferably based on zinc oxide,

- an electrically conductive layer based on silver with a thickness of 6 nm to 9 nm,

- optionally, a blocking layer with a thickness of 0.1 nm to 0.5 nm, preferably based on NiCr,

- a second matching layer with a thickness of 5 nm to 15 nm, preferably 8 nm to 12 nm, preferably based on zinc oxide,

- an anti-reflection layer with a thickness of 25 nm to 40 nm, preferably 30 nm to 35 nm, preferably based on a mixed silicon and metal nitride, such as silicon-zirconium nitride or silicon-hafnium nitride,

- a smoothing layer with a thickness of 5 nm to 10 nm, preferably based on mixed oxide of tin-zinc,

- a first matching layer with a thickness of 5 nm to 15 nm, preferably 8 nm to 12 nm, preferably based on zinc oxide,

- an electrically conductive layer based on silver with a thickness of 6 nm to 10 nm,

- optionally, a blocking layer with a thickness of 0.1 nm to 0.5 nm, preferably based on NiCr,

- a second matching layer with a thickness of 5 nm to 15 nm, preferably 8 nm to 12 nm, preferably based on zinc oxide,

- an anti-reflection layer with a thickness of 70 nm to 90 nm, preferably 75 nm to 80 nm, preferably based on a mixed silicon and metal nitride, such as silicon-zirconium nitride or silicon-hafnium nitride,

- a smoothing layer with a thickness of 5 nm to 10 nm, preferably based on mixed oxide of tin-zinc,

- a first matching layer with a thickness of 5 nm to 15 nm, preferably 8 nm to 12 nm, preferably based on zinc oxide,

- an electrically conductive layer based on silver with a thickness of 6 nm to 9 nm,

- optionally, a blocking layer with a thickness of 0.1 nm to 0.5 nm, preferably based on NiCr,

- a second matching layer with a thickness of 5 nm to 15 nm, preferably 8 nm to 12 nm, preferably based on zinc oxide,

an anti-reflection layer with a thickness of 35 nm to 45 nm, preferably 37 nm to 42 nm, preferably based on a mixed silicon nitride and a metal such as silicon-zirconium nitride or silicon-hafnium nitride.

In one particularly preferred embodiment, the electrically conductive coating comprises or consists of the following layer sequence starting from the substrate:

- an anti-reflective layer based on a mixed silicon and metal nitride, such as silicon-zirconium nitride or silicon-hafnium nitride, with a thickness of 21 nm to 23 nm,

- the first matching layer based on zinc oxide with a thickness of 6 nm to 11 nm,

- an electrically conductive layer based on silver with a thickness of 6.5 nm to 8.5 nm,

- optionally, a blocking layer based on NiCr with a thickness of 0.1 nm to 0.3 nm,

- the second matching layer based on zinc oxide with a thickness of 9 nm to 11 nm,

- an anti-reflective layer based on a mixed silicon nitride and a metal, such as silicon-zirconium nitride or silicon-hafnium nitride with a thickness of 32 nm to 34 nm,

- a smoothing layer based on mixed tin-zinc oxide with a thickness of 6 nm to 8 nm,

- the first matching layer based on zinc oxide with a thickness of 9 nm to 11 nm,

- an electrically conductive layer based on silver with a thickness of 7 nm to 9 nm,

- optionally, a blocking layer based on NiCr with a thickness of 0.1 nm to 0.3 nm,

- the second matching layer based on zinc oxide with a thickness of 9 nm to 11 nm,

- an anti-reflective layer based on a mixed silicon nitride and metal, such as silicon-zirconium nitride or silicon-hafnium nitride, with a thickness of 76.5 nm to 78.5 nm,

- a smoothing layer based on mixed tin-zinc oxide with a thickness of 6 nm to 8 nm,

- the first matching layer based on zinc oxide with a thickness of 9 nm to 11 nm,

- an electrically conductive layer based on silver with a thickness of 6.5 nm to 8.5 nm,

- optionally, a blocking layer based on NiCr with a thickness of 0.1 nm to 0.3 nm,

- the second matching layer based on zinc oxide with a thickness of 9 nm to 11 nm,

- an anti-reflective layer based on a mixed silicon nitride and a metal, such as silicon-zirconium nitride or silicon-hafnium nitride, with a thickness of 38 nm to 40 nm.

When it is said that a layer is based on a material, this means that the layer consists mainly of this material, not counting possible impurities or doping.

The surface resistance of the electrically conductive coating is preferably 1 Ω/□ to 2 Ω/□. With the coating according to the invention, such a surface resistance can be achieved without problems while providing the desired optical properties.

In one embodiment of the invention, the electrically conductive coating is connected to a voltage source to conduct an electrical current through the coating, which is heated as a result. Thus, the laminated glass can be heated. Suitable voltages are, in particular, the on-board voltage usual for the automotive sector, for example 12-14V. It turned out that with the coating according to the invention, very good heating powers can be achieved when connected to a voltage source of 40V-50V, which is common in electric vehicles, for example 42V or 48V. In this way, heating powers of 1500 W/m ² to 5000 W/m ² , in particular 2200 W/m ² to 3000 W/m ² , can be achieved, which is suitable for rapidly removing condensate or freezing from laminated glass. For connection to a voltage source, the coating is preferably provided with power bars which can be connected to the poles of the voltage source in order to inject current into the coating over as much of the width of the glass as possible. The busbars may, for example, be in the form of printed and baked conductors, usually in the form of a fired screen-printing paste with glass frits and silver particles. Alternatively, however, it is also possible to use strips of an electrically conductive film as a busbar, which are applied or glued to a cover, for example copper foil or aluminum foil. Typically, both tires are located near two opposite side edges of the laminated glass, such as the top and bottom edges.

The outer sheet and the inner sheet are preferably made of glass, in particular soda-lime glass, which is common in window panes. However, in principle the sheets can also be made from other types of glass (eg borosilicate glass, quartz glass, aluminosilicate glass) or transparent plastics (eg polymethyl methacrylate or polycarbonate). The thickness of the outer sheet and the inner sheet may vary within wide limits. It is preferable to use sheets with a thickness ranging from 0.8 mm to 5 mm, preferably from 1.4 mm to 2.5 mm, for example with standard thicknesses of 1.6 mm or 2.1 mm.

The outer sheet, inner sheet and thermoplastic interlayer may be transparent and colorless, but may also be tinted or colored. The total light transmission through the laminated glass in one preferred embodiment is greater than 70%. The term total light transmission is based on the method established in ECE-R 43 Annex 3 § 9.1 for testing the light transmission of automotive glass. The outer sheet and the inner sheet may independently be non-hardened, partially hardened or hardened. If at least one of the glass sheets is to be tempered, it may be thermal or chemical tempering. It must be ensured that the electrically conductive coating does not reduce the overall transmission too much.

In addition to being completely transmissive, the laminated glass must also be as color neutral as possible in reflection in order to be perceived as aesthetically pleasing by the user. Reflection colors are typically characterized in the La*b* color space, at 8° and 60° incidence angles to the surface normal, using a D65 illuminant and a 10° viewing angle. It has turned out that with the coating according to the invention it is possible to obtain laminated glasses without too much color distorting shade. At an angle of incidence of 8°, a* is preferably -4 to 0 and b* is -13 to -3. At an angle of incidence of 60°, a* is preferably -2 to 2 and b* is -9 to 1. Such glasses have a discolouration tint that is sufficiently subtle to be suitable for use in the automotive industry.

The laminated glass is preferably curved in one or more spatial directions, as is typical for automotive glass, with radii of curvature typically ranging from about 10 cm to about 40 m. However, the laminated glass may also be flat, for example when provided for buses, trains or tractors.

The thermoplastic intermediate layer contains at least one thermoplastic polymer, preferably ethylene vinyl acetate (EVA), polyvinyl butyral (PVB) or polyurethane (PU), or mixtures, copolymers or derivatives thereof, particularly preferably contains PVB. The intermediate layer is typically formed from a thermoplastic film. The thickness of the intermediate layer is preferably 0.2 mm to 2 mm, particularly preferably 0.3 mm to 1 mm.

Laminated glass can be produced by known methods. The outer sheet and the inner sheet are laminated to each other by means of an intermediate layer, for example, by an autoclaving method, a vacuum bag method, a vacuum ring method, a calendering method, a vacuum lamination, or a combination thereof. In this case, the connection of the outer sheet and the inner sheet is usually carried out under the influence of heat, vacuum and/or pressure.

The electrically conductive coating is applied to the inner sheet, preferably by physical vapor deposition (PVD), particularly preferably by cathodic sputtering, most preferably magnetically assisted cathodic sputtering. The coating is preferably applied to the sheets prior to lamination. Instead of applying an electrically conductive coating to the surface of the glass sheets, it can in principle be applied to a carrier film which is in the intermediate layer.

If the laminated glass is to be convex, then the outer sheet and the inner sheet are subjected to a bending process, preferably before lamination and preferably after possible coating processes. Preferably, the outer sheet and the inner sheet are bent congruently together (i.e. simultaneously and on the same machine), since the sheets will thus be optimally matched for subsequent lamination. Typical temperatures for glass bending processes are, for example, 500°C to 700°C. This heat treatment also increases the transparency and reduces the surface resistance of the conductive coating.

The invention also relates to the use of a laminated glass formed according to the invention as a projection surface of a projection device for a HUD display, the projector being directed towards the HUD area and its radiation being p-polarised. The preferred embodiments described above are appropriate for the application.

In addition, the invention relates to the use of a projection device according to the invention as a HUD in an automobile, in particular a car or truck.

Further, the invention is explained in more detail in the drawings and exemplary embodiments. The drawings are schematic and are not drawn to scale. The drawings do not limit the invention in any way.

On the drawings:

fig. one top view of laminated glass in a typical projection device, fig. 2 sectional view of a typical projection device, fig. 3 sectional view of the laminated glass in the projection device according to the invention, fig. 4 a sectional view of an electrically conductive coating according to the invention, and fig. five reflectance spectrum of p-polarized radiation for laminated glass with an electrically conductive coating according to the invention and for two comparative examples.

Figures 1 and 2 show a detail of a typical HUD projection device. The projection device contains a laminated glass 10, in particular the windshield of a car. In addition, the projection device includes a projector 4 aimed at zone B of the laminated glass 10. In zone B, which is usually called the HUD zone, images can be created by the projector 4, which the viewer 5 (driver) perceives as virtual images on the opposite side of the laminated glass. 10 when his eyes are inside the so-called eye zone E.

The laminated glass 10 consists of an outer sheet 1 and an inner sheet 2, which are connected to each other by an intermediate thermoplastic layer 3. Its lower edge U is located at the bottom in the direction of the car engine, and its upper edge O is at the top in the direction of the roof. The outer sheet 1 in the installed position faces the external environment, and the inner sheet 2 into the vehicle interior.

In FIG. 3 shows an embodiment of a laminated glass 10 made in accordance with the invention. The outer sheet 1 has an outer surface I, which, in the installed position, faces the outside, and an inner surface II, which, in the installed position, faces the inside of the cab. In addition, the inner sheet 2 has an outer surface III, which, in the installed position, faces the outside, and an inner surface IV, which, in the installed position, faces the interior of the passenger compartment. The outer sheet 1 and the inner sheet 2 consist of, for example, soda-lime glass. The outer sheet 1 has, for example, a thickness of 2.1 mm, the inner sheet 2 has a thickness of 1.6 mm. The intermediate layer 3 is formed, for example, from a PVB film with a thickness of 0.76 mm. The PVB film has a substantially constant thickness, apart from the random surface roughness common in the art.

The outer surface III of the inner sheet 2 is provided with an electrically conductive coating 20 according to the invention, which is provided as a reflection surface for projector radiation and furthermore as an IR reflective coating or as a heated coating.

According to the invention, the radiation from the projector 4 is p-polarized, in particular substantially purely p-polarized. Since the projector 4 irradiates the laminated glass 10 at an incidence angle of about 65°, which is close to the Brewster angle, the projector radiation is only slightly reflected from the outer surfaces I, IV of the laminated glass 10. In contrast, the electrically conductive coating 20 according to the invention is optimized to reflect p-polarized radiation . It serves as a reflection surface for the radiation of the projector 4 to create a projection on the windshield.

Fig. 4 shows the sequence of layers in an electrically conductive coating 20 according to the invention. The cover 20 contains three electrically conductive layers 21 (21.1, 21.2, 21.3). Each electrically conductive layer 21 is sandwiched between two of a total of four anti-reflection layers 22 (22.1, 22.2, 22.3, 22.4). In addition, the coating 20 has two smoothing layers 23 (23.2, 23.3), three first matching layers 24 (24.1, 24.2, 24.3), three second matching layers 25 (25.2, 25.3, 25.4) and three blocking layers 26 (26.1, 26.2 , 26.3).

The sequence of layers is shown schematically in the figure. In addition, the sequence of layers of the laminated glass 10 with the coating 20 on the outer surface III of the inner sheet 2 is shown, together with the materials and thicknesses of the individual layers, in Table 1 (example). Table 1 also shows the layer sequence for two comparative examples with four electrically conductive layers 21. Comparative example 2 is an electrically conductive coating already used at present, and comparative example 1 is a coating with a significantly thinner conductive layer 21 compared to it. Layer materials may have alloying, which is not indicated in the table. For example, SnZnO-based layers can be antimony doped, and ZnO, SiN, or SiZrN-based layers can be aluminum doped.

A comparison of the example with comparative example 2 shows that the coating 20 according to the invention is characterized in particular by significantly thinner electrically conductive layers 21. Therefore, the coating 20 according to the invention is cheaper to deposit. However, the electrical conductivity is still high enough to allow the coating 20 according to the invention to be used as a heated coating, in particular in combination with a supply voltage of 40V to 50V. The desired reflection characteristics, the desired surface resistance and other optical properties are set using a suitable dielectric layer structure.

Comparative example 1 has a similar total thickness of all electrically conductive layers 21 as the example according to the invention. However, it is provided by a large number of conductive layers, so that the thickness of the individual layers is less than in the example. Surprisingly, too small a layer thickness leads to an increase in light absorption. This can be avoided with the layered structure according to the invention.

The anti-reflection layers 22 in the example according to the invention are made as individual layers based on silicon zirconium nitride. In comparative examples, the anti-reflection layers are partially separated into two separate layers: one layer based on silicon nitride and one layer based on silicon-zirconium nitride. This separation of the anti-reflection layers can contribute to the reduction of surface resistance and can in principle also be used within the scope of the invention. However, in the present example, this is not necessary to achieve the required laminated glass specifications.

Table 1

Position Materials and layer thicknesses Example Comparative Example 1 Comparative Example 2 one glass glass glass 3 PVB PVB PVB twenty 22.5 - - SiZrN 36.8 nm SiZrN 52.2 nm 25.5 - - ZnO 10.0 nm ZnO 10.0 nm 26.4 - - NiCr 0.1 nm NiCr 0.2 nm 21.4 - - Ag 6.6 nm Ag 14.1 nm 24.4 - - ZnO 10.0 nm ZnO 10.0 nm 23.4 - - SnZnO 7.0 nm SnZnO 7.0 nm 22.4 SiZrN 39.0 nm SiZrN
SiN 23.5 nm
29.8 nm SiZrN
SiN 22.9 nm
29.8 nm 25.4 ZnO 10.0 nm ZnO 10.0 nm ZnO 10.0 nm 26.3 NiCr 0.1 nm NiCr 0.1 nm NiCr 0.2 nm 21.3 Ag 7.5 nm Ag 2.0 nm Ag 14.2 nm 24.3 ZnO 10.0 nm ZnO 10.0 nm ZnO 10.0 nm 23.3 SnZnO 7.0 nm SnZnO 7.0 nm SnZnO 7.0 nm 22.3 SiZrN 77.6 nm SiZrN 12.9 nm SiZrN
SiN 20.1 nm
29.6 nm 25.3 ZnO 10.0 nm ZnO 10.0 nm ZnO 10.0 nm 26.2 NiCr 0.1 nm NiCr 0.1 nm NiCr 0.2 nm 21.2 Ag 8.0 nm Ag 8.5 nm Ag 17.1 nm 24.2 ZnO 10.0 nm ZnO 10.0 nm ZnO 10.0 nm 23.2 SnZnO 7.0 nm SnZnO 7.0 nm SnZnO 7.0 nm 22.2 SiZrN 33.0 nm SiZrN 20.4 nm SiZrN
SiN 19.4 nm
34.1 nm 25.2 ZnO 10.0 nm ZnO 10.0 nm ZnO 10.0 nm 26.1 NiCr 0.1 nm NiCr 0.1 nm NiCr 0.2 nm 21.1 Ag 7.5 nm Ag 6.0 nm Ag 11.7 nm 24.1 ZnO 10.0 nm ZnO 10.0 nm ZnO 10.0 nm 22.1 SiZrN 21.8 nm SiN 20.6 nm SiN 28.8 nm 2 glass glass glass 1.6 nm

Fig. 5 shows the reflectance spectrum of laminated glass with a conventional conductive coating 20, as in the comparative examples, and with a conductive coating 20 according to the invention, as in the example, for p-polarized radiation (see Table 1). The spectra were taken inside the cabin at an angle of incidence of 65°, thus simulating the reflection characteristics of a HUD projector. Both illustrations in the figure differ only in the scale of the ordinate.

Compared to comparative example 2, the example according to the invention has, firstly, a higher average reflection in the corresponding spectral range, and secondly, is smoother than the comparative example. The result is a more intense and color-neutral projection image on the windshield.

Comparative Example 1 and Example have similar reflectance in the respective spectral range and similar smoothness. Therefore, Comparative Example 1 is also suitable for projecting on a windshield with p-polarized light. However, the thin layers of silver in Comparative Example 1 unexpectedly reduce light transmission through the laminated glass, which can be critical in the case of windshields.

For the example according to the invention, the degree of reflection is at least 13% over the entire spectral range of 450-650 nm, for comparative example 1 at least 15%, and for comparative example 2 values of only 3% are also observed. For example, the difference between the maximum observed reflectance and the average reflectance is 0%, and the difference between the minimum observed reflectance and the average reflectance in the spectral range of 450-650 nm is 1%. For Comparative Example 1, the corresponding values are 1% and 0%, and for Comparative Example 2, 7% and 6%.

Table 2 lists some optical parameters of laminated glass according to the invention (example from table 1) and comparative glass (comparative example 1 from table 1) familiar to the skilled person and commonly used to characterize automotive glasses. RL stands for total light reflection and TL for total light transmission (according to ISO 9050). The information after RL or TL indicates the light source used, where A means light source A and HUD means HUD projector with 473nm, 550nm and 630nm (RGB) emission wavelengths. The given angle values after the type of light radiation mean the angle of incidence of the radiation relative to the normal to the outer surface. Thus, an angle of incidence less than 90° indicates irradiation outside the cabin, and an angle of incidence greater than 90° indicates irradiation inside. The specified angle of incidence of 115° corresponds to an angle of incidence relative to the normal to the inner surface of 65° (=180°-115°) and simulates the irradiation of the projector according to the invention. Below the reflection parameters are the corresponding color coordinates a* and b* in the L*a*b* color system, followed by a description of the light source used (D65 light source and HUD projector) and data on the viewing angle (the angle at which the light beam hits the retina).

The ISO 13837 TTS designation stands for total radiated solar energy measured according to ISO 13837 and is a measure of thermal comfort.

The total reflection values and color coordinates for both glasses are close. The reflection of the p-polarized radiation from the HUD projector from the inside is high enough to guarantee a high intensity HUD projection. At the same time, the colors are relatively neutral when reflected from the outside, so that the laminated glass does not have an unpleasant color-distorting tint. The example according to the invention, due to its thicker silver layer, has a markedly higher light transmission, which is advantageous for use as a windshield.

The surface resistance of the coating 20 was 1.5 Ω/□, so that with a supply voltage of, for example, 42V and a typical windshield height (busbar spacing), a heating power of approximately 2300 W/m ² can be achieved.

table 2

Example Comparative Example 1 RL A 8° /% 16.8 16.9 a* (D65/10°) -1.9 -2.0 b* (D65/10°) -9.5 -5.0 RL A 60° /% 21.8 22.3 a* (D65/10°) 0.7 1.1 b* (D65/10°) -5.1 -2.6 RL HUD p-pol. 115° /% 14.2 15.2 a* (HUD/10°) -0.8 -1.0 b* (HUD/10°) -0.2 0.2 TL A 0° /% 73.0 71.6 TTS ISO 13837 /% 56.0 53.4

List of positions for links:

(10) laminated glass (one) outer sheet (2) inner sheet (3) thermoplastic intermediate layer (4) projector (five) observer / driver (twenty) conductive coating (21) electrically conductive layer (21.1), (21.2), (21.3), (21.4) 1.,2.,3.,4. electrically conductive layer (22) anti-reflective layer (22.1), (22.2), (22.3), (22.4), (22.5) 1.,2.,3.,4.,5. anti-reflective layer (23) smoothing layer (23.2), (23.3), (23.4) 1., 2., 3. smoothing layer (24) first matching layer (24.1), (24.2), (24.3), (24.4) 1.,2.,3.,4. first matching layer (25) second matching layer (25.2), (25.3), (25.4), (25.5) 1.,2.,3.,4. second matching layer (26) blocking layer (26.1), (26.2), (26.3), (26.4) 1., 2., 3., 4. blocking layer (o) top edge of laminated glass 10 (U) bottom edge of laminated glass 10 (B) laminated glass HUD zone 10 (E) eye area (I) outer, facing from the intermediate layer 3, the surface of the outer sheet 1 (II) inner, facing the intermediate layer 3 surface of the outer sheet 1 (III) outer facing the intermediate layer 3 surface of the inner sheet 2 (iv) inner, facing away from the intermediate layer 3, the surface of the inner sheet 2

Claims (27)

1. A projection device for a head-up display (HUD), comprising at least - laminated glass (10) with a HUD zone (B), containing an outer sheet (1) and an inner sheet (2), which are connected to each other by a thermoplastic intermediate layer (3), and the outer surfaces (I, IV) of the laminated glass (10 ) are parallel to each other; - an electrically conductive coating (20) on the surface (II, III) of the outer sheet (1) or inner sheet (2) facing the intermediate layer (3) or in the intermediate layer (3), wherein the electrically conductive coating (20) has a surface resistance of 1 ohm/□ up to 2 ohm/□; And - a projector (4) aimed at the HUD area (B); moreover, the radiation of the projector is (4) p-polarized and falls on the laminated glass (10) with an angle of incidence from 60° to 70°, moreover, laminated glass (10) with an electrically conductive coating (20) in the entire spectral range of 450-650 nm has a degree of reflection of p-polarized radiation from 10% to 20%, moreover, the electrically conductive coating (20) contains at least three electrically conductive layers (21), each of which is located between two dielectric layers or sequences of dielectric layers, each dielectric layer or sequence of dielectric layers contains at least one anti-reflection layer, and moreover, the sum of the thicknesses of all electrically conductive layers (21) is not more than 30 nm, and while the electrically conductive layers (21) have a thickness of 5 nm to 10 nm. 2. The projection device according to claim. 1, and the laminated glass (10) with an electrically conductive coating (20) in the entire spectral range of 450-650 nm has a degree of reflection of p-polarized radiation of at least 12%. 3. The projection device according to claim. 1 or 2, and the difference between the maximum observed degree of reflection and the average value of the degree of reflection, as well as the difference between the minimum observed degree of reflection and the average value of the degree of reflection of p-polarized radiation in the spectral range 450-650 nm does not exceed 5%, preferably does not exceed 3%, particularly preferably does not exceed 1%. 4. The projection device according to one of paragraphs. 1-3, wherein the sum of the thicknesses of all electrically conductive layers (21) is between 15 nm and 30 nm, preferably between 20 nm and 25 nm. 5. The projection device according to one of paragraphs. 1-4, the electrically conductive layers (21) having a thickness of 7 nm to 8 nm. 6. The projection device according to one of paragraphs. 1-5, wherein the electrically conductive layers (21) are based on silver. 7. The projection device according to one of paragraphs. 1-6, each sequence of dielectric layers contains an anti-reflection layer (22), and moreover - the anti-reflection layer (22.1) under the first conductive layer (21.1) has a thickness of 15 nm to 25 nm, preferably 20 nm to 24 nm, - the anti-reflection layer (22.2) between the first conductive layer (21.1) and the second conductive layer (21.2) has a thickness of 25 nm to 40 nm, preferably 30 nm to 35 nm, - the anti-reflection layer (22.3) between the second conductive layer (21.2) and the third conductive layer (21.3) has a thickness of 70 nm to 90 nm, preferably 75 nm to 80 nm, the anti-reflection layer (22.4) above the third conductive layer (21.3) has a thickness of 35 nm to 45 nm, preferably 37 nm to 42 nm. 8. The projection device according to claim 7, wherein the anti-reflection layers (22) are based on a mixed silicon and metal nitride, such as silicon-zirconium nitride or silicon-hafnium nitride. 9. The projection device according to one of paragraphs. 1-8, and between the two electrically conductive layers (21) is a sequence of dielectric layers, which contains - an anti-reflective layer (22) based on silicon nitride (SiN), mixed silicon and metal nitrides such as silicon-zirconium nitride (SiZrN), aluminum nitride (AlN) or tin oxide (SnO), - a smoothing layer (23) based on an oxide of one or more elements selected from tin, silicon, titanium, zirconium, hafnium, zinc, gallium and indium, - the first and second matching layers (24, 25) based on zinc oxide and optionally, a blocking layer (26) based on niobium, titanium, nickel, chromium and/or their alloys. 10. The projection device according to one of paragraphs. 1-9, and the radiation of the projector (4) is essentially purely p-polarized. 11. The projection device according to one of paragraphs. 1-10, wherein the electrically conductive coating (20) is connected to a 40-50 V voltage source to heat the laminated glass. 12. The use of a projection device according to one of paragraphs. 1-11 as a HUD in a vehicle, such as a car or truck.

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